Rietberg was first mentioned as 'Rietbike' around the year 1100. This name refers to Ried which is an old name for reed and to 'Bach' which means creek. There was a castle that dated back to the 11th century. From 1237, it was home to the family of Wenzel Adam von Kaunitz, Count Rietberg. From this time on the part 'Berg' in the name Rietberg refers to the existence of a castle which is called 'Burg' in German. Since that time Rietberg was an independent German territory until the year 1807. In the Middle Ages the Rietberg county was a very small state. Nevertheless, Rietberg had its own militia, its own currency and its own laws. Even foreign policy, on a small scale, was conducted independently. Until the 17th century Rietberg coined its own money.